When my car is idling around 1000rpm, I can hear some rattling noise from the bottom of the car sort of like the two pieces of metal rubbing against each other hard and vibrating at the same time. It goes away sometimes. Is the catback causing this problem? or could it be the exhaust hitting the suspension piece? Plz help

 

im sorry but that is a little vague. it could be coming from anywhere underneath your car....be more specific

 

It could be a lot of things, but you're very lucky that it happens at idle. I would put the car up on jackstands or ramps level and start the car, then carefully roll around underneath on my creeper board. Wear leather gloves and start poking around. (Start with the exhaust first so you can check that out before it becomes nuclear-hot)

David

 

First guess is loose heat-shielding somewhere....turbos or cat. At idle, the vibration resonance is just right to make noise.

 

Why haven't you got under the car and shaked the exhaust and look for the problem?
Instead of checking you only complain and ask. Time for you to try being a mechanic.